In recent years, hybrid cars driven by using both an engine and an electric motor have become widespread. In such a hybrid car, a high-voltage battery whose voltage is higher than that of a low-voltage battery for starting-up the engine is mounted, and a direct current supplied from the high-voltage battery is inverted to an alternating current by an inverter and then is supplied to the electric motor.
In regard to a vehicle in which the high-voltage battery is mounted, it is preferable that a flow of current between the inverter and the high-voltage battery is blocked in advance in order to allow maintenance to be performed safely. Therefore, there is disclosed a power supply circuit in which a service plug (blocking member), which is manually detachable, is interposed between the inverter and the high-voltage battery, and the service plug is detached by a worker at the time of the maintenance to block the flow of current between the inverter and the high-voltage battery (for example, PTL 1).
FIG. 2 shows an example of the above-described power supply circuit. As shown in the same figure, the power supply circuit 100 includes a battery pack 101 disposed at the rear of the vehicle, an inverter 102 and a motor 103 that are disposed at the front of the vehicle as a load, an ECU 104 that is disposed at the front of the vehicle as a relay control unit that controls an operation of the inverter 102 and the motor 103. A high-voltage battery 105 is built in the battery pack 101, and a direct current supplied from the high-voltage-battery 105 is converted to an alternating current power source by the inverter 102 and is supplied to the motor 103.
In addition, three relays 106 provided between the high-voltage battery 105 and the inverter 102 are built in the battery pack 101. Both ends of a relay coil C provided to each of the relays 106 are connected to the ECU 104. The ECU 104 controls the current passing through the relay coil C and thereby controls the turning on and off of a contact point S of each of the relays 106.
The high-voltage battery 105 is an assembled battery in which batteries of a plurality of batteries are connected to each other in series, and a service plug 107 is provided between the batteries. The service plug 107 is detachably provided between the batteries making up the high-voltage battery 105. When the service plug is detached, a supply of power from the high-voltage battery 105 to the inverter 102 and the motor 103 is blocked and when the service plug is attached, the supply of power from the high-voltage battery 105 to the inverter 102 and the motor 103 is enabled. The service plug 107 is provided with an interlock switch 108 that detects the attachment and detachment of the service plug 107.
The interlock switch 108 is turned off when the service plug 107 is detached, and is turned on when the service plug 107 is attached. The ECU 104 is connected to the interlock switch 108 with the inverter 102 and the motor 103 interposed therebetween, determines that the service plug 107 is detached when the interlock switch 108 is turned off, and blocks the current flowing through the relay coil C and turns off the relay 106. Therefore, it is possible to more reliably block the supply of power from the high-voltage battery 105 to the inverter 102 and the motor 103.